Q: A compound microscope has a 10x ocular lens and a 40x objective lens. What is the total magnification, and how is it calculated?

Total magnification is $10 \times 40 = 400$; multiply ocular and objective magnifications.

Q: If the field diameter at 10x objective is 2 mm, what is the field diameter at 40x objective? Use the formula $\text{Field Diameter}_{\text{new}} = \frac{\text{Field Diameter}_{\text{old}} \times \text{Magnification}_{\text{old}}}{\text{Magnification}_{\text{new}}}$.

Field diameter at 40x is $\frac{2 \times 10}{40} = 0.5$ mm.

Question 1

Which part of the compound light microscope should you avoid adjusting when any objective other than the scanning objective is over the stage, and why?

Accepted Answer

The coarse focus knob, because it can damage the slide or objective lens.

Question 2

A compound microscope has a 10x ocular lens and a 40x objective lens. What is the total magnification, and how is it calculated?

Accepted Answer

Total magnification is $10 	imes 40 = 400$; multiply ocular and objective magnifications.

Question 3

If the field diameter at 10x objective is 2 mm, what is the field diameter at 40x objective? Use the formula $	ext{Field Diameter}_{	ext{new}} = \frac{	ext{Field Diameter}_{	ext{old}} 	imes 	ext{Magnification}_{	ext{old}}}{	ext{Magnification}_{	ext{new}}}$.

Accepted Answer

Field diameter at 40x is $\frac{2 	imes 10}{40} = 0.5$ mm.

Question 4

What is the purpose of oil immersion in microscopy, and how does it improve resolution?

Accepted Answer

Oil immersion increases the numerical aperture by reducing light refraction, improving resolution.

Question 5

A bacterial cell measures $0.1$ microns. If the resolving power of your microscope is $0.2$ microns, can you see the cell? Use $	ext{Resolving Power} = \frac{\lambda}{2 	imes 	ext{NA}}$.

Accepted Answer

No, because the cell is smaller than the resolving power; objects smaller than $0.2$ microns cannot be resolved.

Question 6

Which of the following best describes the difference between positive and negative staining?

Accepted Answer

Positive staining colors the cells, while negative staining colors the background.

Question 7

Why are most biological stains composed of salts, and what happens when they are dissolved in water?

Accepted Answer

Salts dissociate into cations and anions, allowing the chromophore to bind to cellular structures.

Question 8

During Gram-staining, what is the most critical step, and what can happen if it is performed incorrectly?

Accepted Answer

The decolorizer step; too long causes all cells to appear Gram-negative, too short causes all cells to appear Gram-positive.

Question 9

Which structural feature distinguishes Gram-positive from Gram-negative bacteria, and how does this affect staining?

Accepted Answer

Gram-positive bacteria have a thick peptidoglycan layer, retaining crystal violet and staining purple.

Question 10

A patient’s specimen smear shows bacterial cells accompanied by WBCs. What does this indicate?

Accepted Answer

The presence of WBCs suggests an active immune response, indicating infection.

Question 11

Which domain and kingdom are bacteria classified in?

Accepted Answer

Domain Bacteria, Kingdom Bacteria.

Question 12

Which microorganism is observed as a ring-shaped structure inside human RBCs and is responsible for malaria?

Accepted Answer

Plasmodium species.

Question 13

Which motility structure is found in Paramecium, and to which domain and kingdom does it belong?

Accepted Answer

Cilia; Domain Eukarya, Kingdom Protista.

Question 14

Which microorganism is transmitted by a biological vector and causes African sleeping sickness?

Accepted Answer

Trypanosoma species, transmitted by the tsetse fly.

Question 15

What is the main difference between prokaryotic and eukaryotic cells when viewed under a microscope?

Accepted Answer

Eukaryotic cells have a nucleus and organelles; prokaryotic cells lack these structures.

Question 16

Why is it important to use saline instead of water when preparing a wet mount of live bacteria?

Accepted Answer

Saline maintains osmotic balance, preventing cell lysis.

Question 17

Which of the following is a limitation of using a wet prep instead of a prepared smear slide?

Accepted Answer

Wet preps lack staining, making it difficult to distinguish cellular structures.

Question 18

Yeast cells display which type of asexual reproduction, and how can you recognize this under the microscope?

Accepted Answer

Budding; visible as small daughter cells attached to the parent cell.

Question 19

If you observe a bread mold under the microscope, which structure should you look for to help identify the type of mold?

Accepted Answer

The arrangement and shape of sporangia and hyphae.

Question 20

Which equation is used to calculate resolving power, and what does a smaller value indicate?

Accepted Answer

Resolving power is calculated as $	ext{Resolving Power} = \frac{\lambda}{2 	imes 	ext{NA}}$; a smaller value indicates better resolution.

Microbiology Lab Exam 1 Study Guide: Key Concepts and Procedures

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